4 c4 was played by Leonhart as long ago as the last last century, but it was Alekhine and Botvinnik who, by elaborating on Panov's groundwork, eventually developed it into a true system. Indeed, the variation is also commonly known as the Panov-Botvinnik attack.

4 ... Nf6

The most natural answer and the most common in practice: ... dxc4 or ... e6 can be played later, so Black avoids committing himself immediately. The only deviation of real significance here is 4 ... Nc6!? after which White can transpose to other lines by way of 5 Nf3 Bg4 6 Nc3 Nf6, while the continuation 5 Nc3 e5! gives Black acceptable play according to Schwartz: 6 cxd5! Nxd4 7 f4 f6 8 Nf3 +=

Stronger, however, is 5 cxd5! Qxd5 6 Nf3 transposing to a minor variation of the Sicilian defence that favours White.

5 Nc3 ...

5 c5!? g6 6 Nc3 Bg7 7 Bb5+ Nc6 8 Nge2 0-0 9 0-0Mariotti-Savon, Venice 1974, 9 ... Bd7 ∞. This position after 5 Nc3 is the basic starting point of the Panov. The most frequent continuations are now 5 ... Nc6 and 5 ... e6 and may be analyzed in subsequent nodes.

5 ... g6

The bishop's development on the flank is logical, but a bit slow. In most instances, Black has to sacrifice his d5 pawn, at least temporarily, in order to complete his development. The most popular continuations for White at this point are 6 cxd5 and 6 Qb3.